1. Field of the Invention
The invention pertains to a method for the fabrication, on a plane substrate, of a microswitch actuatable by a magnetic field. The invention also pertains to a microswitch of this kind.
Microswitches actuatable by a magnetic field are also called Reed switches.
Microswitches differ from macroscopic switches inter alia by their method of fabrication. The microswitches are made by using the same batch manufacturing methods as those used to make microelectronic chips. For example, the microswitches are made with a monocrystalline silicon or glass machined by photolithography and etching and/or structured by epitaxial growth and deposition of metallic material.
Prior art micro-switches comprise:                a plane substrate having an upper face,        at least two strips of magnetic material having vertical faces that extend in parallel to the plane of the substrate and mutually define an air gap, at least one of the strips being capable of being shifted under the effect of the magnetic field, between:                    a closed position in which the vertical faces of the two strips are directly in mechanical contact with each other to enable the passage of current, and            an open position in which the vertical faces are separated from each other by the air gap to electrically insulate one strip from the other.                        
In these known microswitches, the shifting of the strips is done in parallel to the plane of the substrate. Thus, during the fabrication of these microswitches, the thickness of the strips parallel to the plane of the substrate can be defined very precisely by photolithography with almost no limitation. This enables the very fine and repeatable adjustment of certain important properties of the microswitch, such as for example, the rigidity of these strips. These advantages cannot be found in microswitches where the strips are shifted perpendicularly to the plane of the substrate.
2. Prior Art
Methods for fabricating these microswitches have already been proposed, for example in the patent application US 2009/0237188 or in the following article (article A1): S. Roth, C. Marxer, G. Feusier, N. F. De Rooij, “One mask nickel micro-fabricated reed relay”, IEE 0-7803-5273-4, 2000.
However, the known methods are complex and call for a large number of etching steps. For example, the method of fabrication described in the article A1 requires an operation of etching a photosensitive resin to hollow out and release the vertical faces of the strips and another etching operation to eliminate a seeding layer situated between the strips.
Besides, in the prior-art microswitches, the strips project onto the upper face of the substrate. It is therefore necessary to add a hood to protect them. Now, this operation is complicated because it calls for high precision in the positioning of the hood relatively to the substrate.
In the prior art, the following are also known: JP2008243450A, US2007/046392A1, WO98/34269A1 and EP1108677A1.